Study On Preparation And Thermal Properties Of Fatty Acids Phase Change Microcapsules

With the increase of energy demand,energy crisis has become a difficult problem in the world.Therefore,improving the efficiency of energy utilization and developing new renewable energy sources have become a major issue at present.Phase change materials(PCMs)can release and store a large amount of latent heat in the process of phase change and the temperature is basically unchanged.It has become a commonly used material in the field of thermal energy storage,but it has the shortcoming of easy leakage.The preparation of microencapsulated phase change materials(MPCMs)can not only solve the leakage of PCMs,but also increase the heat transfer area,avoid the PCMs contact with the outside world and restrict the flow of PCMs.In this paper,novel mono and binary fatty acids phase change microcapsules were prepared,which can prevent the leakage of PCMs while maintaining high latent heat of phase change.In addition,the synthesized microcapsules were mixed with phosphogypsum to prepare phosphogypsum based phase change composites and it can play a certain role in energy saving and consumption reduction when used in the building envelope.(1)The lauric acid/silica phase change microcapsules were prepared by interfacial polymerization,and the effects of core-shell mass ratio,emulsifier dosage,emulsification speed,pH and reaction time on the encapsulation effect of the MPCMs were investigated.The optimum synthesis conditions were determined as follows:core-shell mass ratio 2:1,emulsifier dosage 0.8 g,emulsification speed 1000 r/min,pH 2.0and reaction time 10 h.The MPCM prepared under these conditions had regular spherical structure,latent heat of melting was 182.2 J/g,encapsulation rate and encapsulation efficiency were 78.3%and 78.6%,respectively.Infrared spectrometer(FT-IR)and X-ray diffractometer(XRD)showed that the lauric acid and silica were combined through physical interaction without chemical reaction during the coating process.The results of thermogravimetric analysis(TGA)and leakage analysis showed that the prepared microcapsules had good thermal energy storage capacity and high temperature stability below 210?,and no obvious leakage during the phase change process.(2)Microencapsulated phase change materials were prepared by interfacial polymerization using lauric acid-stearic acid binary eutectic as core material and silica as shell material.Taking the encapsulation effect as inspection index,the optimal synthesis conditions of MPCMs were determined by single factor experiment and orthogonal experiment as follows:core-shell ratio 1:1,emulsifier dosage 0.9 g,emulsification time 1 h,droplet acceleration rate of hydrolysis 6 m L/min and reaction temperature 60?.The characterization results showed that the core material and shell material of the MPCM were tightly combined with a smooth spherical surface.The latent heat of melting and solidification were 170.3 J/g and 155.7 J/g,respectively,and the encapsulation rate and encapsulation efficiency were 80.9%and 81.1%,respectively.The microcapsule had excellent thermal properties.In addition,the leakage of lauric acid-stearic acid was also solved due to the protection of the SiO₂shell.(3)Retarder and glass fiber were added to phosphogypsum to improve its cementing properties and mechanical strength.The results showed that when the dosage of retarder was 0.1%and the amount of glass fiber was 0.1%,the compressive strength of phosphogypsum was 17.23 MPa,which was increased by 58.5%compared with the original phosphogypsum.The treated phosphogypsum and the prepared lauric acid-stearic acid/silica phase change microcapsules were blended in different proportions to prepare the phosphogypsum based phase change composites.The characterization results showed that when the MPCM content was 50 wt%,the compressive strength of the composite was 5.66 MPa,and the latent heat of melting and solidification were 70.1 J/g and 67.8 J/g,respectively,which can be used in the construction field to reduce the indoor temperature fluctuation.